A gas probe having such a sensor element is described in German Patent Application No. DE 198 57 468, for example, for use in analyzing the exhaust gas of internal combustion engines. In a conventional manner, the elongated planar sensor element is arranged in a housing that can be affixed in a measuring orifice of an exhaust pipe. On the measuring side, at an end that is exposed to the exhaust gas, the sensor element has a measuring device, which includes an electrochemical cell having a first electrode, a second electrode and a solid electrolyte situated between the first and second electrode. The first electrode is arranged in a reference-gas region introduced in the sensor element. The second electrode is mounted on an outer surface of the sensor element and is in contact with the exhaust gas via a porous protective layer.
A heating device is provided to heat the measuring device. The heating device has a meander-shaped heater (resistance heater) to which a first and a second heater supply lead are guided. The heater supply leads electrically connect the heater, which is arranged on the measuring-side end of the sensor element, to contact surfaces provided on a connection-side end lying across from the measuring-side end of the sensor element and via which the heater is electrically connected to electrical circuit elements arranged outside of the gas sensor. The heater and the two heater supply leads are arranged in a plane of stratification of the sensor element. The two heater supply leads extend in parallel to the longitudinal axis of the sensor element. Insulation layers electrically insulate the heating device from the surrounding elements.
The heater is operated in a conventional manner by the electrical circuit elements applying a voltage between the two heater supply leads. The first heater supply lead is at a constant potential, such as earth potential. Conventionally, the temperature inside the measuring device is determined with the aid of a resistance measurement, for example, and to control the heating device with the aid of the electrical circuit elements in such a way that a predefined temperature value is given inside the measuring device. The control-related potential changes at the second heater supply lead may interfere with the function of the measuring device because of induced voltage. Therefore, an electron-conducting intermediate layer, made of platinum, for example, is provided between the heating device and the measuring device, the intermediate layer being at a constant electrical potential.
It is disadvantageous in this context that the layer configuration for reducing the voltages which the heating device induces into the measuring device is expensive to produce and the additional platinum layer is costly.